s51dude: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/s51dude - from package: s51dude

You may install the required package with command apt-get install {package}

Error in other languages:
s51dude: bevel nie gevind nie
s51dude: comandă negăsită
s51dude: comando não encontrado
s51dude: commande introuvable
s51dude: command not found
s51dude: käsku ei ole
s51dude: không tìm thấy lệnh
s51dude: komanda nerasta
s51dude: Kommando nicht gefunden.
s51dude: kommandot finns inte
s51dude: komut yok
s51dude: nie znaleziono polecenia
s51dude: níor aimsíodh an t-ordú
s51dude: no se encontró la orden
s51dude: no s'ha trobat l'ordre
s51dude: opdracht niet gevonden
s51dude: parancs nem található
s51dude: perintah tidak ditemukan
s51dude: príkaz nenájdený
s51dude: příkaz nenalezen
s51dude: команда не найдена
s51dude: командата не е открита
s51dude: 命令找不到
s51dude: コマンドが見つかりません